1. Field of the Invention
The present invention relates to a backlight unit for use disposed behind a display panel to illuminate the display panel with light, and specifically relates to a backlight unit for use disposed behind a display panel to illuminate the display panel with light that includes on its lamp housing surface a plurality of tubular lamps that are a light source held by lamp holders while the tubular lamps are arranged in parallel provided with predetermined intervals therebetween.
2. Description of the Related Art
In recent years, liquid crystal display devices are in widespread use as flat-screen display devices. Among them, liquid crystal display devices used for television devices and other display devices each include a liquid crystal display panel arranged to display an image, and a backlight unit disposed behind the liquid crystal display panel. The backlight unit includes a plurality of tubular lamps such as CCFLs (Cold Cathode Fluorescent Lamp) that are alight source, and is arranged to illuminate the liquid crystal display panel from behind with light emitted from the lamps while controlling the properties of the emitted light. The light illuminating the display panel passes through the display panel, making an image displayed visible on a front side of the liquid crystal display panel.
FIG. 10 is a view showing a schematic configuration of a conventional liquid crystal display device. As shown in FIG. 10, a liquid crystal display device 60 includes a liquid crystal display panel 61 arranged to display an image, and a backlight unit 62 disposed behind the display panel 61.
The backlight unit 62 includes a backlight chassis 63 substantially in the shape of a box of low height, and a plurality of CCFLs 64 arranged in parallel in the backlight chassis 63, a reflection sheet 65, and optical sheets 66. Light emitted from the CCFLs 64 passes, together with light reflected by the reflection sheet 65, through the optical sheets 66 and the display panel 61, and is visually perceived from the observer's side. The optical sheets 66 are arranged to adjust the properties of the light entering the display panel 61 from the CCFLs 64.
FIG. 11 is a front view of the backlight unit 62. As shown in FIG. 11, the CCFLs 64 are arranged in parallel such that the intervals provided between the adjacent CCFLs 64 are narrow at the middle portion of the backlight chassis 63 and become wider toward each top and bottom end of the backlight chassis 63 in order to maximize the luminance at the middle portion of a screen of the display panel 61 and gradually decrease the luminance toward the ends of the screen, which is disclosed in Japanese Patent Publication Laid-Open No. Hei06-75216. This arrangement is used because the number of the CCFLs 64 can be reduced compared with a conventional arrangement of CCFLs while the luminance of the screen is not visually perceived to be irregular with human eyes.
In this arrangement, the CCFLs 64 are held by lamp holders 67 and 68, as disclosed in Japanese Patent Publication Laid-Open No. 2001-210126, on a lamp housing surface of the backlight chassis 63 as shown in FIG. 11. Having a long tubular length, the CCFLs 64 cannot be positioned with assured positioning accuracy only by being held at their both ends by electrode holders 69, so that the CCFLs 64 are held also at their midway by the lamp holders 67 and 68.
In this arrangement, the lamp holders 67 and 68 that are of two different kinds and shown respectively in FIGS. 12A and 12B are used in order to provide narrow intervals between the adjacent CCFLs 64 at the middle portions of the backlight chassis 63 and wide intervals between the adjacent CCFLs 64 at each top and bottom end of the backlight chassis 63. The lamp holder 67 includes a holder board 70 having a rectangular shape, and two lamp holding members 72 disposed at both end portions of the holder board 70. The lamp holder 68 includes a holder board 71 having a rectangular shape, and two lamp holding members 72 disposed at both end portions of the holder board 71. The lamp holding members 72 each have the shape of a ring with an opening atop thereof so as to hold the CCFL 64.
In addition, the lamp holders 67 and 68 each include a sheet supporting pin 73 having a stick shape. The sheet supporting pins 73 are provided in a protruding manner between the lamp holding members 72 from the holder boards 70 and 71, and each have a length such that the optical sheets 66 are made apart at a predetermined distance from the reflection sheet 65. Having such a configuration, the sheet supporting pins 73 can prevent the optical sheets 66, which are disposed top of the backlight unit 62, from being deformed to bend downward, minimizing occurrence of luminance irregularity on the display panel 61. The lamp holders 67 and 68 include mounting members 74 under the lamp holding members 72, and are arranged to be fixed to the backlight chassis 63 by engaging the mounting members 74 in mounting openings 75 provided in the reflection sheet 65 and the backlight chassis 63.
However, there is a problem that manufacturing costs are not easily reduced because the components that constitute the backlight unit 62 increase in number since the two different kinds of lamp holders 67 and 68 that have different distances between the lamp holding members 72 as shown in FIGS. 12A and 12B need to be used in order to provide the narrow intervals between the adjacent CCFLs 64 at the middle portions of the backlight chassis 63 and the wide intervals between the adjacent CCFLs 64 at each top and bottom end of the backlight chassis 63.